Fermentation processes are used commercially at large scale to produce organic molecules such as ethanol, citric acid and lactic acid. In those processes, a carbohydrate is fed to a organism that is capable of metabolizing it to the desired fermentation product. The carbohydrate and organism are selected together so that the organism is capable of efficiently digesting the carbohydrate to form the product that is desired in good yield. It is becoming more common to use genetically engineered organisms in these processes, in order to optimize yields and process variables, or to enable particular carbohydrates to be metabolized.
Starch is a widely available and inexpensive carbohydrate source. It is available from a wide variety of plant sources such as corn, wheat, rice, barley, and the like. Many organisms are not capable of metabolizing starch directly, or else metabolize it slowly and inefficiently. Accordingly, it is common to treat starch before feeding it into the fermentation process, in order to break it down into monosaccharides that the organism can ferment easily.
Usually, starch is hydrolyzed to form a mixture containing mainly glucose (i.e., dextrose). However, complete hydrolysis to glucose adds significant cost, so most commercially available glucose products tend to contain a small amount of various oligomeric polysaccharides. Unfortunately, many organisms cannot metabolize the oligomers, either, and so these carbohydrate values are wasted.